Mobile electronic devices such as smartphone and tablet computers support powerful, versatile computing and communication. These mobile electronic devices can run thousands of different software applications (“apps”), which are a great convenience to users. However, a limitation of such devices lies in the display technology. In order to provide readability in low to moderate light conditions smartphones and tablets use emissive displays, such LCDs or Active Matrix Organic Light Emitting Diode (AMOLED) displays.
Given the efficiency of such displays in converting electrical energy to visible light and given the limited electrical energy storage (e.g., battery capacity) of portable devices, as a practical matter there is an imposed limit on the brightness and usage per charge of LCD and AMOLED displays. The brightness limits become problematic when using the devices outdoors on bright sunny days. Under such ambient lighting conditions, the unwanted inherent reflectivity of the display in combination with the high ambient light illuminance on the display surface may lead to the displayed image or text being ‘washed out’ and difficult to see.
In the past, transflective displays have been used on a limited basis. Like other LCD displays, a transflective display includes a 2-D array of pixels and each pixel includes multiple subpixels, for example red, blue and green subpixels. In a transflective display, each subpixel is divided into two parts such that it includes a reflective part and a transmissive part. As in other LCD displays, electric voltages are used to alter the configuration (e.g., the molecular long axis orientation) of the liquid crystals in the display to modulate the passage of light through the display. In the reflective portion, light traverses the liquid crystal twice—once going in and once going out after reflection. On the other hand in the transmissive portion, light from a back light located behind the display traverses the liquid crystal only once on the way out of the display.
Recently there has been a trend toward very high resolution displays. Pixel densities greater than 300 pixels per inch (ppi) are not uncommon and significantly higher pixel densities are on the horizon. Therefore a solution that provides the benefits of transflective displays and is adaptable for high pixel densities is desirable.